Except at the lowest levels of incorporation of one resin in the other, thermoplastic polyurethane (herein TPU) and polyolefin (herein PO) are intrinsically incompatible. It has been suggested that TPU/PO blends might offer advantages in terms of cost, mechanical properties, hydrolytic and thermal stability, stain and solvent resistance, and good adhesion to polyolefin substrates and efforts to make these components compatible one with the other have been reported. Blends made with conventional processing equipment, such as a twin screw extruder, tend to separate during the melt blending procedure into the individual phases. The separation is believed attributable to the large differences in solubility parameters between these resins, resulting in the creation of interfacial tension between the non-polar polyolefin and highly polar polyurethane. As a consequence of separation, the blends display poor physical properties. This incompatibility is manifested by either the lowering of some measured physical property to a value below that for either one of the components, or by visual observation of separation (for instance, fracture or crumbling). The difficulty in preparing relevant blends, especially blends containing more than 30% polyurethane, has been disclosed in the article "Polyurethane-Polypropylene Blends", Z. S. Petrovic et al in J. Appl. Polym. Sci. 42, 1991 pp. 779. U.S. Pat. No. 3,272,890 discloses blends of polyurethane and polyethylene. The method of preparation of the blend entails melting and fluxing the polyethylene in a Banbury mixer and then adding the polyurethane. Systems containing dispersed polyethylene in polyurethane have been disclosed in U.S. Pat. Nos. 3,310,604; 3,351,676; and 3,358,052; other relevant blends having improved processability have been disclosed in U.S. Pat. No. 3,929,928.
U.S. Pat. Nos. 4,410,595 and 4,423,185 disclose compositions containing thermoplastic polyurethanes and polyolefins, the later being modified with functional groups including carboxylic acid anhydride. Japanese Patent Application 74,9831 (Derwent Abstract 242I6V) discloses modified ionomer polymer blends containing polyurethane and polyethylene.
Relevant block copolymers have been disclosed in U.S. Pat. Nos. 4,499,238 and 5,256,734. The '734 patent disclosed a composition containing 100 parts of polypropylene and 20 to 100 parts of hydrogenated styrene/butadiene or styrene isoprene elastomeric block copolymers. The composition is understood to provide molded articles having low mold shrinkage and linear expansion coefficient. Relevant block copolymers have also been disclosed in U.S. Pat. Nos. 5,187,236; 5,198,495; 5,034,449; and 5,248,729.
The preparation of a multi-component polymer blend containing a polyurethane, a specifically structured, selectively hydrogenated, monoalkenyl arene-diene block copolymer and a dissimilar engineering resin has been disclosed in U.S. Pat. No 4,107,131. Polyolefin is among the dissimilar resins. Plastic compositions containing a polyamide, a functionalized polyolefin and an acid-grafted elastomer have been disclosed in U.S. Pat. No. 4,795,782. Also relevant for their disclosure of block copolymers as compositional components of thermoplastic molding compositions are U.S. Pat. Nos. 4,429,076; 4,906,687 and 4,939,207.
Of particular relevance in the present context is U.S. Pat. No. 4,883,837 which disclosed compatible compositions containing a polyolefin, a thermoplastic polyurethane and as a compatibilizing agent, a modified polyolefin. The modified polyolefin thus disclosed is an olefinic copolymer containing functional groups. Further of particular relevance are U.S. Pat. Nos. 4,107,131 and 4,088,627 which disclosed compatibilized TPU compositions containing polyolefins and relevant compatibilizing agents.